Anti-fog coating composition

ABSTRACT

Provided is an anti-fog coating composition that rarely suffers from blushing when applied and dried even under high-humidity conditions and that can be heat-cured even at low temperature in a short time and form a coating film that exhibits excellent tight adhesion to a substrate and excellent heat resistance and anti-fog properties. The anti-fog coating composition comprises (A) a copolymer prepared from a monomer mixture of a monomer (A1), a monomer (A2) and a monomer (A3); (B) a basic compound such as amines; and (C) a surfactant such as anionic surfactants. The monomer (A1) is a vinyl monomer that has an N-methylol group or an N-alkoxymethylol group. The monomer (A2) is a vinyl monomer that has a sulfonic acid group. The monomer (A3) is an alkyl(meth)acrylate monomer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No.PCT/JP2010/073020, filed on Dec. 21, 2010, which claims priority fromJapanese Patent Application No. 2010-002817, filed on Jan. 8, 2010, thecontents of all of which are incorporated herein by reference in theirentirety.

TECHNICAL FIELD

The present invention relates to an anti-fog coating composition that isformed on a substrate such as an automobile headlamp, that does notsuffer from blushing and other problems even when applied and driedunder high-humidity conditions, and that can be heat-cured in a shorttime and at a low temperature to form a coating film with tight adhesionto the substrate and excellent heat resistance and anti-fog properties.

BACKGROUND ART

In automobile headlamps and other vehicular lighting fixtures, fogoccurs when high-humidity air enters the light chamber, the lens iscooled by outside air, rainfall or the like, and moisture condenses onthe inner surface. This reduces the brightness of the vehicular lamp,and can also make the lens less attractive, causing userdissatisfaction. Anti-fog coatings that are coated on the areas wherefog occurs are known as a means of preventing such fogging of the lens.

The applicants in this case have already proposed a heat-cured anti-fogcoating composition such as the following (see Patent Document 1). Thisheat-cured anti-fog coating composition contains a monomer having across-linkable functional group that is either a N-methylol group, aN-methylol ether group or a hydroxyl group, and a block or graftcopolymer consisting of a hydrophilic polymer part formed from ahydrophilic monomer and a lower alkyl(meth)acrylate and a hydrophobicpolymer part formed from a vinyl monomer having a sulfonic acid,carboxyl or phosphoric acid group and a lower alkyl(meth)acrylate. Withthis anti-fog coating composition, it is possible to form a coating filmwhereby excellent anti-fog properties and adhesiveness are maintained inhigh-temperature environments.

-   Patent Document 1: Japanese Patent Application Laid-open No.    H6-212146 (page 2, page 3, pages 14 to 17)

SUMMARY OF INVENTION

However, with the anti-fog coating composition of Patent Document 1 along curing time of 60 minutes is required to heat-cure the coating filmat a low temperature of 80° C. Another problem is blushing attributableto the hydrophobic polymer part of the copolymer, which occurs if therelative humidity (RH) of the environment exceeds 60% when the anti-fogcoating composition is applied, and often causes whitening of the coatedfilm. Blushing is a phenomenon that occurs when the humidity is high(such as RH 60% or more) when a coating material is applied and dried,in which fine particles of moisture in the air condense on the surfaceof the coating film during application and drying, and the resincomponents aggregate and precipitate, resulting in bumps andindentations on the surface of the coating film that cause the coatingfilm to appear white.

It is an object of the present invention to provide an anti-fog coatingcomposition whereby blushing is suppressed even when a coating materialis applied and dried under high-humidity conditions, and which can beheat-cured in a short time and at a low temperature to obtain a coatingfilm with tight adhesion to a substrate and excellent heat resistanceand anti-fog properties.

To achieve this object, the anti-fog coating composition of one aspectof the present invention contains a copolymer (A) formed from a monomermixture containing a monomer (A1), a monomer (A2) and a monomer (A3); abasic compound (B); and a surfactant (C). The monomer (A1) is vinylmonomer having N-methylol group or N-alkoxymethylol group. The monomer(A2) is vinyl monomer having sulfonic acid group. The monomer (A3) isalkyl(meth)acrylate monomer.

Preferably, the content of the monomer (A1) is 3 to 20 parts by mass,the content of the monomer (A2) is 3 to 20 parts by mass, the content ofthe monomer (A3) is 60 to 94 parts by mass, and the total of themonomers (A1) and (A2) is 6 to 40 parts by mass per 100 parts by mass asthe total of the monomers (A1), (A2) and (A3), while the content of thebasic compound (B) is 50 to 90 mol % of the sulfonic acid group in themonomer (A2), and the content of the surfactant (C) is 0.5 to 30 partsby mass per 100 parts by mass of the copolymer (A).

Preferably, the monomer mixture further contains aN,N-dialkyl(meth)acrylamide monomer (A4), the content of the monomer(A4) being 5 to 50 parts by mass per 100 parts by mass as the combinedcontent of the monomers (A3) and (A4).

The base dissociation constant of the basic compound (B) in an aqueoussolution at 25° C. is preferably 3 to 14.

The boiling point of the basic compound (B) is preferably 130 to 1500°C.

In one example, the copolymer (A) has crosslinked structures formed by acondensation reaction of N-methylol group or N-alkoxymethylol group ofthe monomer (A1), and the monomer (A2) has neutralized sulfonic acidgroup that improves the hydrophilicity and heat resistance of thecopolymer (A) and non-neutralized sulfonic acid group that promotes thecondensation reaction of the monomer (A1).

The following effects can be achieved with the present invention.

With the anti-fog coating composition of the first invention, goodcuring properties are achieved based on the properties of the monomer(A1), while accelerated curing at low temperatures and blushingsuppression are achieved based on the properties of the monomer (A2),and good heat resistance and adhesiveness with the substrate areachieved based on the properties of the monomer (A3) forming thecopolymer. Moreover, neutralizing some of the sulfonic acid groups ofthe monomer (A2) based on the properties of the basic compound (B)serves to increase the hydrophilicity of the copolymer while alsoenhancing the blushing suppression effect and providing excellent heatresistance by suppressing oxidation degradation of the coating filmcaused by sulfonic acid groups under high temperature conditions.Additionally, good anti-fog properties are achieved by the surfactanteffect of the surfactant (C), which reduces the surface tension of themoisture adhering to the coating film surface so that it forms a waterfilm.

Thus, with the anti-fog coating composition blushing is suppressed evenwhen the coating material is applied and dried under high-humidityconditions, and heat-curing can be achieved in a short time and at a lowtemperature to obtain a coating film with tight adhesion to a substrateand excellent heat resistance and anti-fog properties.

BEST MODE FOR CARRYING OUT THE INVENTION

Detailed embodiments of the present invention are explained in detailbelow.

<Anti-Fog Coating Composition>

The anti-fog coating composition of this embodiment contains a copolymer(A) formed from a monomer mixture containing a monomer (A1), a monomer(A2) and a monomer (A3); a basic compound (B); and a surfactant (C). Themonomer (A1) is vinyl monomer having N-methylol group (—NHCH₂OH) orN-alkoxymethylol group (—NHCH₂OR, where R is alkyl group). The monomer(A2) is vinyl monomer having sulfonic acid group (sulfo group, —SO₃H).The monomer (A3) is alkyl(meth)acrylate monomer.

This anti-fog coating composition can be used favorable as an anti-fogcoating material for headlamps and other vehicular lighting fixtures forexample. This anti-fog coating composition does not suffer from blushingand other problems when applied and dried under high-humidityconditions, and can be heat-cured in a short time and at a lowtemperature. A coating film obtained by heat-curing the anti-fog coatingcomposition has tight adhesion to a substrate (object to be coated), andexcellent heat resistance and anti-fog properties.

The components of the anti-fog coating composition are sequentiallyexplained order below.

[Copolymer (A)]

[Monomer (A1)]

The monomer (A1) forming the copolymer, or in other words a vinylmonomer having N-methylol or N-alkoxymethylol group, is explained first.This monomer (A1) is a vinyl monomer for forming crosslinked structuresin the copolymer by intermolecular crosslinking in a dehydrationcondensation reaction, dealcoholization condensation reaction or othercondensation reaction. Because the monomer (A1) has such cross-linkablefunctional groups, crosslinked structures are formed in the copolymerwhen it is heated after manufacture. This condensation reaction ispromoted by an acid catalyst.

Examples of the monomer (A1) include N-methylol(meth)acrylamide,N-methoxymethylol(meth)acrylamide and N-butoxymethylol(meth)acrylamidefor example. One or two or more of these can be used as the monomer(A1). Of these monomers, N-methylol(meth)acrylamide is particularlydesirable as the monomer (A1) from the standpoint of excellent storagestability of the anti-fog coating composition and excellent heat-curingproperties at low temperatures.

The content of the monomer (A1) is 3 to 20 parts by mass or preferably 5to 15 parts by mass per 100 parts by mass as the total of the monomers(A1), (A2) and (A3). If the content of the monomer (A1) is less than 3parts by mass, the low-temperature curing properties of the copolymerare reduced, and the curing time is prolonged. If the content of themonomer (A1) exceeds 20 parts by mass, on the other hand, thecrosslinking density of the copolymer is increased, reducing theanti-fog properties of the coating film, and the crosslinking reactionmay progress over time if the film is left under high-temperatureconditions, further reducing the anti-fog properties of the film.

[Monomer (A2)]

The monomer (A2), or in other words a vinyl monomer having sulfonic acidgroup, is explained next. This monomer (A2) functions as an acidcatalyst to promote the condensation reaction of the monomer (A1) at lowtemperatures, and also serves to give the coating film a good externalappearance by increasing the hydrophilicity of the copolymer andsuppressing blushing when the composition is applied and dried underhigh humidity conditions.

Examples of the monomer (A2) include 3-sulfopropyl(meth)acrylate,2-sulfoethyl(meth)acrylate, 2-acrylamido-2-methylpropanesulfonic acid,p-styrenesulfonic acid, vinylsulfonic acid and methallylsulfonic acidfor example. One or two or more of these can be used as the monomer(A2).

Of these monomers, 3-sulfopropyl(meth)acrylate,2-sulfoethyl(meth)acrylate and 2-acrylamido-2-methylpropanesulfonic acidare particularly desirable as the monomer (A2) from the standpoint ofexcellent copolymerizability with the monomer (A1).

The content of the monomer (A2) is preferably 3 to 20 parts by mass ormore preferably 5 to 15 parts by mass per 100 parts by mass as the totalof the monomers (A1), (A2) and (A3). If the content of the monomer (A2)is less than 3 parts by mass, it does not function sufficiently as anacid catalyst in the condensation reaction of the monomer (A1), so thatthe low-temperature curing properties of the copolymer are reduced andthe curing time tends to be longer. The copolymer also becomesinsufficiently hydrophilic, and there is a risk of blushing when thecomposition is applied and dried under high humidity conditions. On theother hand, if the content of the monomer (A2) exceeds 20 parts by massthe polarity of the copolymer (A) is much higher, and the adhesivenessof the coating film tends to be less because affinity between thecoating film and the substrate reduced, while at the same time the heatresistance of the coating film tends to be less because there is anincreased risk of oxidation degradation of the coating film caused bysulfonic acid groups of the monomer (A2) under high-temperatureconditions.

[Monomer (A3)]

The monomer (A3), which is an alkyl(meth)acrylate monomer, is explainednext. This monomer (A3) is a component that enhances the heat resistanceof the coating film and confers good adhesiveness by increasing theaffinity between the coating film and the substrate. Alkyl(meth)acrylatemonomers are linear, branched or cyclic alkyl esters of (meth)acrylicacid.

Examples of this monomer (A3) include methyl(meth)acrylate,ethyl(meth)acrylate, n-propyl(meth)acrylate, isopropyl(meth)acrylate,n-butyl(meth)acrylate, isobutyl(meth)acrylate, t-butyl(meth)acrylate,2-ethylhexyl(meth)acrylate, lauryl(meth)acrylate, stearyl(meth)acrylateand cyclohexyl(meth)acrylate. One or two or more of these may be used asthe monomer (A3).

A lower alkyl(meth)acrylate monomer is preferred as monomer (A3). Thelower alkyl(meth)acrylate monomers are those alkyl(meth)acrylatemonomers in which the number of carbon atoms in the alkyl group of thealkyl ester is 1 to 4. A lower alkyl(meth)acrylate in which the alkylgroup of the alkyl ester has 1 or 2 carbon atoms is preferred as monomer(A3). When using an alkyl(meth)acrylate in which the alkyl group of thealkyl ester has 5 or more carbon atoms, the hydrophilicity of thecopolymer is reduced, and there is an increased risk of blushing whenthe composition is applied and dried under conditions of high humidity.

The content of the monomer (A3) is preferably 60 to 94 parts by mass ormore preferably 70 to 90 parts by mass per 100 parts by mass as thetotal of the monomers (A1), (A2) and (A3). If the content of the monomer(A3) is less than 60 parts by mass, adhesiveness between the coatingfilm and the substrate is reduced due to the increased proportions ofthe monomers (A1) and (A2). If the content of the monomer (A3) exceeds94 parts by mass, on the other hand, the low-temperature curingproperties of the copolymer are less due to the decreased proportions ofmonomers (A1) and (A2), and the curing time tends to be longer.

[Other Vinyl Monomer]

Another vinyl monomer can be used as a monomer for forming the copolymerin addition to the monomer (A1), monomer (A2) and monomer (A3). Thisother vinyl monomer is not particularly limited as long as it can becopolymerized with the monomers (A1) to (A3).

Specific examples of the other vinyl monomer include styrene, vinyltoluene, α-methylstyrene and other aromatic vinyl monomers;(methoxy)polyethylene glycol mono(meth)acrylate, (methoxy)polypropyleneglycol mono(meth)acrylate, (ethoxy)polyethylene glycolmono(meth)acrylate, (ethoxy)polypropylene glycol mono(meth)acrylate andother alkoxy alkylene glycol(meth)acrylate monomers;2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl(meth)acrylate,4-hydroxybutyl(meth)acrylate, 2-hydroxyethyl(meth)acrylateε-caprolactone adduct and other hydroxyl group-containing vinylmonomers; (meth)acrylic acid, crotonic acid, maleic acid, maleic acidhalf ester and other carboxyl group-containing monomers and their alkalimetal salts and ammonium salts; and (meth)acrylamide,N-methyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide,N-ethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide,N-n-propyl(meth)acrylamide, N-isopropyl(meth)acrylamide,N-dimethylaminoethyl(meth)acrylamide, N-dimethylaminopropyl(meth)acrylamide, diacetone(meth)acrylamide, N-(meth)acryloylpiperidine, (meth)acryloyl morpholine, N-vinyl-2-pyrrolidone, 2-vinylpyridine and other nitrogen atom-containing vinyl monomers and the like.One or two or more of these can be used as the other vinyl monomer.

[Monomer (A4)]

Of these other vinyl monomers, N,N-dimethyl(meth)acrylamide,N,N-diethyl(meth)acrylamide or another N,N-dialkyl(meth)acrylamidemonomer (sometimes abbreviated as monomer (A4)) is preferred from thestandpoint of superior heat resistance, high hydrophilicity, and goodblushing suppression effects. One or two or more monomers (A4) may beused. The content of the monomer (A4) is preferably 5 to 50 parts bymass per 100 parts by mass as the total of the monomers (A3) and (A4).

From the standpoint of excellent heat resistance and adhesiveness to thesubstrate and also for improving hydrophilicity of the copolymer andsuppressing blushing, it is especially desirable to use a combination ofa lower alkyl(meth)acrylate monomer (A3) and a N,N-dialkyl acrylamidemonomer (A4).

When a lower alkyl(meth)acrylate monomer is used in combination with aN,N-dialkyl(meth)acrylamide monomer, the content of the loweralkyl(meth)acrylate monomer (A3) is preferably 50 to 90 parts by masswhile the content of the N,N-dialkyl(meth)acrylamide monomer (A4) issuch as to constitute the remainder per 100 parts by mass as the totalof the lower alkyl(meth)acrylate monomer (A3) and theN,N-dialkyl(meth)acrylamide monomer (A4). If the content of the loweralkyl(meth)acrylate monomer (A3) is less than 50 parts by mass, thecuring time required to obtain a sufficient degree of crosslinking islonger because the copolymer is much more hydrophilic. On the otherhand, if the content of the lower alkyl(meth)acrylate monomer (A3)exceeds 90 parts by mass, the effect of increasing the hydrophilicity ofthe copolymer is reduced, and the blushing suppression effect tends tobe less.

[Method of Manufacturing Copolymer (A)]

Copolymer (A) can be obtained by copolymerizing a monomer mixture of theaforementioned monomers (A1), (A2) and (A3), together with monomer (A4)as necessary. The copolymer structure can be a random copolymer,alternating copolymer, block copolymer or graft copolymer structure, buta random copolymer is preferred from the standpoint of ease ofpreparation, and for improving the anti-fog properties and other effectsof the anti-fog coating composition. A radical polymerization method,cationic polymerization method, anionic living polymerization method,cationic living polymerization method or other known polymerizationmethod can be adopted as the polymerization method for obtaining thecopolymer, but a radical polymerization method is preferred for ease ofindustrial production in particular, and for reasons of performance inevery sense. A common bulk polymerization method, suspensionpolymerization method, emulsion polymerization method or the like can beadopted as the radical polymerization method, but a solutionpolymerization method is preferred because the composition can then beused as is as a coating material after polymerization.

A manufacturing method using solution polymerization is explained below.

If the polymerization solvent has a very high boiling point, the tightadhesion between the coating film and the substrate may be adverselyaffected by residual polymerization solvent remaining from drying andheat-curing of the coating film, so it is desirable to use apolymerization solvent with a boiling point of less than 180° C.Examples of such polymerization solvents include methanol, ethanol,n-propanol, isopropanol, n-butanol, isobutanol, s-butanol, t-butanol,diacetone alcohol and other alcohol solvents; ethylene glycol monomethylether, ethylene glycol monethyl ether, propylene glycol monomethylether, propylene glycol monoethyl ether, 3-methoxy-1-butanol,3-methoxy-3-methyl-1-butanol and other alcohol ether solvents; acetone,methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone and otherketone solvents; tetrahydrofuran, dioxane and other ether solvents;methyl acetate, ethyl acetate, n-butyl acetate, isobutyl acetate,t-butyl acetate, methyl lactate, ethyl lactate and other ester solvents;benzene, toluene, xylene and other aromatic solvents; formamide,dimethyl formamide and other amide solvents; and water and the like. Oneor two or more of these polymerization solvents may be used.

The total amount of the monomers is preferably 50 parts by mass or lessper 100 parts by mass as the combined amount of the polymerizationsolvent used in the polymerization reaction plus the total amount of themonomers (A1), (A2) and (A3), and monomer (A4) as necessary. If theratio of monomers is over 50 parts by mass, more polymerization heat isgenerated, and industrial manufacture tends to be difficult.

A commonly used organic peroxide, azo compound or the like can be usedas a radical polymerization initiator. Examples of organic peroxidesinclude benzoyl peroxide, 3,5,5-trimethyl hexanoyl peroxide,t-butylperoxy-2-hexanoato-, t-butyl peroxypivalate, t-hexylperoxypivalate and the like. Examples of azo compounds include2,2′-azobis isobutyronitrile, 2,2′-azobis-2-methylbutyronitrile and thelike. The added amount of the radical polymerization initiator ispreferably 0.01 to 5 parts by mass per total 100 parts mass of themonomers (A1), (A2) and (A3) with monomer (A4) as necessary. To controlpolymerization heat generation, it is desirable drip a radicalpolymerization initiator into the reaction container to perform thepolymerization reaction. The polymerization temperature can be changedappropriately according to the kind of radical polymerization initiatorused, but is preferably 30 to 150° C. or more preferably 40 to 100° C.for purposes of industrial manufacture.

[Basic Compound (B)]

Next, basic compound (B) is explained. This basic compound is acomponent that neutralizes part of the sulfonic acid groups in themonomer (A2). Neutralizing part of the sulfonic acid groups in themonomer (A2) with basic compound (B) serves to increase thehydrophilicity of the copolymer and enhance the blushing suppressioneffect, while also suppressing oxidation degradation of the coating filmcaused by sulfonic acid groups in high-temperature environments, therebyimproving heat resistance.

Examples of the basic compound (B) include sodium hydroxide, calciumhydroxide, ammonia, methylamine, dimethylamine, trimethylamine,ethylamine, diethylamine, triethylamine, monoethanolamine,diethanolamine, triethanolamine, dimethylaminoethanol,diethylaminoethanol, aniline, α-naphthylamine, benzylamine, pyridine,2,6-lutidine, imidazole and the like. One or two or more of these may beused as the basic compound (B).

To facilitate dissociation from sulfonic acid groups during heat-curingof the coating film and to prevent interference with the acid catalysteffect of the sulfonic acid groups, the base dissociation constant(hereunder abbreviated as pKb) of the basic compound (B) in an aqueoussolution at 25° C. is preferably 3 to 14, or more preferably 4 to 14.Examples of such basic compounds (B) include ammonia (pKb=4.7),methylamine (pKb=3.5), dimethylamine (pKb=3.4), trimethylamine(pKb=3.2), ethylamine (pKb=3.5), diethylamine (pKb=3.4), triethylamine(pKb=3.2), monoethanolamine (pKb=4.5), diethanolamine (pKb=5.1),triethanolamine (pKb=6.2), dimethylaminoethanol (pKb=4.1),diethylaminoethanol (pKb=4.1), aniline (pKb=4.6), α-naphthylamine(pKb=10.1), benzylamine (pKb=4.6), pyridine (pKb=8.8), 2,6-lutidine(pKb=8.0), imidazole (pKb=7.1) and the like.

In order to achieve a greater suppression effect on oxidationdegradation of the coating film caused by sulfonic acid groups underhigh-temperature conditions, basic compound (B) preferably has a boilingpoint of 130 to 1500° C. and low volatility in high-temperatureenvironments, and more preferably has a boiling point of 150 to 1500° C.Examples of this basic compound (B) include sodium hydroxide (boilingpoint 1390° C.), calcium hydroxide (degrades at melting point 580° C.),monoethanolamine (boiling point 172° C.), diethanolamine (boiling point217° C.), triethanolamine (boiling point 335° C.), dimethylaminoethanol(boiling point 144° C.), diethylaminoethanol (boiling point 163° C.),aniline (boiling point 184° C.), α-naphthylamine (boiling point 301°C.), benzylamine (boiling point 183° C.), 2,6-lutidine (boiling point144° C.) and imidazole (boiling point 256° C.).

A compound having a pKb of 3 to 14 in an aqueous solution at 25° C. anda boiling point of 130 to 1500° C. is especially desirable as the basiccompound (B). Examples of this basic compound (B) includemonoethanolamine, diethanolamine, triethanolamine, dimethylaminoethanol,diethylaminoethanol, imidazole and the like.

A compound having a pKb of 4 to 14 at 25° C. and a boiling point of 150to 1500° C. is most desirable as the basic compound (B). Examples ofthis basic compound (B) include monoethanolamine, diethanolamine,triethanolamine, diethylaminoethanol, imidazole and the like.

The content of the basic compound (B) is determined so that this basiccompound (B) neutralizes part of the sulfonic acid groups of the monomer(A2), leaving the monomer (A2) with both sulfonic acid groups thatimprove the hydrophilicity and heat resistance of copolymer (A) andnon-neutralized sulfonic acid groups that promote the condensationreaction of the monomer (A1). In an embodiment, the content of the basiccompound (B) is 50 to 95 mol % or preferably 60 to 90 mol % of thesulfonic acid groups in the monomer (A2). If the content of the basiccompound (B) is less than 50 mol %, the effect of improving thehydrophilicity and heat resistance of the copolymer is less. On theother hand, it is undesirable for the content of the basic compound (B)to exceed 95 mol % because the acid catalyst function of the sulfonicacid groups is reduced, and the low-temperature curing properties of thecopolymer are greatly diminished.

The method of neutralizing the sulfonic acid groups of monomer (A2) withthe basic compound (B) may be either a method of adding the basiccompound (B) to a solution of the copolymer and a solvent, or a methodof adding basic compound (B) together with the monomers whenmanufacturing the copolymer. Of these, the latter method is preferredbecause acidity is reduced when monomer (A2) is neutralized with basiccompound (B), thereby providing good solubility in the polymerizationsolvent and reducing the likelihood of corrosion of the reactioncontainer.

[Surfactant (C)]

The surfactant (C) is explained next. The surfactant (C) is a componentthat reduces the surface tension of the moisture adhering to the coatingfilm surface, forming a water film on the coating film surface andthereby improving the anti-fog properties. The surfactant (C) may be anyconventionally known surfactant, and examples include non-ionicsurfactants, anionic surfactants, cationic surfactants, amphotericsurfactants and the like. Of these, it is desirable to include at leastone or more anionic surfactants in order to achieve lasting effects.

Examples of non-ionic surfactants include polyoxyethylene laurylalcohol, polyoxyethylene lauryl ether, polyoxyethylene oleyl ether andother polyoxyethylene higher alcohol ethers, polyoxyethylene octylphenol, polyoxyethylene nonyl phenol and other polyoxyethylene alkylaryl ethers, polyoxyethylene glycol monostearate and otherpolyoxyethylene acyl esters, polypropylene glycol ethylene oxide adduct,polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitanmonostearate and other polyoxyethylene sorbitan fatty acid esters, andalkyl phosphate ester, polyoxyethylene alkyl ether phosphate ester andother phosphate esters, sugar esters and cellulose esters for example.

Examples of anionic surfactants include sodium oleate, potassium oleateand other fatty acid salts, sodium lauryl sulfate, ammonium laurylsulfate and other higher alcohol sulfate esters, dodecylbenzene sodiumsulfonate, sodium alkyl naphthalene sulfonate and other alkyl benzenesulfonic acid salts and alkyl naphthalene sulfonic acid salts, condensedformalin naphthalene sulfonate, dialkyl sulfosuccinate salts, dialkylphosphate salts, sodium polyoxyethylene alkyl phenyl ether sulfate andother polyoxyethylene sulfate salts and the like for example.

Examples of cationic surfactants include ethanolamines, laurylamineacetate, triethanolamine monoformate, stearamide ethyl diethylamineacetate and other amine salts, lauryl trimethyl ammonium chloride,stearyl trimethyl ammonium chloride, dilauryl dimethyl ammoniumchloride, distearyl dimethyl ammonium chloride, lauryl dimethyl benzylammonium chloride, stearyl dimethyl benzyl ammonium chloride and otherquaternary ammonium salts and the like for example.

Examples of amphoteric surfactants include dimethyl alkyl laurylbetaine, dimethyl alkyl stearyl betaine and other fatty acid-basedamphoteric surfactants, dimethyl alkyl sulfobetaine and other sulfonicacid-based amphoteric surfactants, and alkyl glycine and the like forexample.

The content of these surfactants (C) is preferably 0.5 to 30 parts bymass or more preferably 1 to 20 parts by mass per 100 parts by mass ofthe copolymer. If the content of the surfactant (C) is less than 0.5parts by mass, it is difficult to obtain long-lasting continuousanti-fog properties of the coating film. If it exceeds 30 parts by mass,on the other hand, the external appearance and tight adhesiveness of thecoating film are diminished, and the water resistance of the coatingfilm also tends to be less. The method of mixing the copolymer and thesurfactant (C) may be a method of adding the surfactant (C) to asolution of the copolymer dissolved in a solvent, or a method of addingthe surfactant (C) together with the monomers during manufacture of thecopolymer.

[Other Components]

The essential components of the anti-fog coating composition are thecopolymer (A), the basic compound (B) and the surfactant (C). Variouscommonly used additives such as leveling agents, anti-oxidants, UVabsorbents, light stabilizers, curing catalysts and the like can also becompounded as other components in the anti-fog coating composition.These other components can be compounded in the commonly used amountsfor each additive.

[Preparation of Anti-Fog Coating Composition]

The anti-fog coating composition is generally manufactured by adding asolvent to dissolve, disperse or dilute a solution of the copolymerobtained by copolymerization of the aforementioned monomers, with theaim of adjusting the viscosity for coating purposes. Because the tightadhesion between the coating film and the substrate may be adverselyaffected by residual solvent remaining from drying and heat-curing ofthe coating film if the solvent has an extremely high boiling point, thesolvent added to the copolymer solution preferably has a boiling pointof less than 180° C.

Examples of such solvents include methanol, ethanol, n-propanol,isopropanol, n-butanol, isobutanol, s-butanol, t-butanol, diacetonealcohol and other alcohol solvents; ethylene glycol monomethyl ether,ethylene glycol monethyl ether, propylene glycol monomethyl ether,propylene glycol monoethyl ether, 3-methoxy-1-butanol,3-methoxy-3-methyl-1-butanol and other alcohol ether solvent; acetone,methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone and otherketone solvents; tetrahydrofuran, dioxane and other ether solvents;methyl acetate, ethyl acetate, n-butyl acetate, isobutyl acetate,t-butyl acetate, methyl lactate, ethyl lactate and other ester solvents;benzene, toluene, xylene and other aromatic solvents; formamide,dimethyl formamide and other amide solvents; n-hexane, cyclohexane,n-heptane, n-octane, n-decane and other hydrocarbon solvents; and waterand the like. One or two or more of these may be used as the solvent.

[Coated Article]

A coated article formed using this anti-fog coating composition isexplained here. This coated article is formed by applying and drying theanti-fog coating composition on an object to be coated as the substrate,and then heat-curing for 5 to 60 minutes at 60 to 150° C. to therebyform a coating film on the surface of the object to be coated.

As the specific method of forming the coating film, the anti-fog coatingcomposition is first applied to the object to be coated by anapplication method used with ordinary coating materials. The surface ofthe object to be coated is preferably first cleaned of adheringcontaminants, degreased and washed before application with the aim ofincreasing the wetting properties of the anti-fog coating composition onthe object to be coated and preventing repellence. Specific examples ofthis include dust removal with high-pressure air or ionized air,ultrasonic cleaning with an aqueous detergent solution or alcoholsolvent, wiping with an alcohol solvent or the like, and UV or ozonecleaning and the like. Suitable application methods include dipping,flow coating, roll coating, bar coating, spray coating and the like.

After application, the coating film is dried by volatilizing the solventfor 0.5 to 5 minutes at a temperature of 20 to 50° C. Next, the coatingfilm is formed by heat-curing for 5 to 60 minutes at a temperature of 60to 150° C., or preferably for 10 to 40 minutes at a temperature of 70 to130° C. During this process, the sulfonic acid groups of the monomer(A2) promote a dehydration condensation reaction or dealcoholizationcondensation reaction of the N-methylol groups or N-alkoxymethylolgroups of the monomer (A1) in the copolymer, forming crosslinkedstructures in the copolymer. However, when the object to be coated is asynthetic resin material, it is necessary to set the curing temperatureto a temperature at or below the thermal deformation temperature of thesynthetic resin material.

The film thickness of the coating film formed on the object to be coatedwith the anti-fog coating composition is preferably 0.5 to 20 μm or morepreferably 1 to 10 μm in order to obtain good anti-fog properties and agood external appearance of the coating film. If this coating film isthinner than 0.5 μm the anti-fog properties of the coating film tend tobe less, while if it is thicker than 20 μm the external appearance ofthe coating film tends to be poor.

Films, plates and molded articles of acrylic resin, polycarbonate resin,polyethylene terephthalate resin and other transparent resins, andworked articles of these, can preferably be used for the object to becoated with the anti-fog coating composition. A vehicular lightingfixture is especially desirable as this object to be coated. Specificexamples of vehicular lighting fixtures include headlights, auxiliaryheadlights, road lights, license-plate lights, tail lights, parkinglights, brake lights, back-up lights, turn indicator lights, auxiliaryturn indicator lights, hazard flashers and the like.

Summary of Effects of Embodiment

(1) With the anti-fog coating composition of the embodiment, good curingproperties are obtained due to the properties of the monomer (A1), whileaccelerated curing at low temperatures and blushing suppression areachieved due to the properties of the monomer (A2), and good heatresistance and adhesiveness with the substrate are achieved due to theproperties of the monomer (A3). Moreover, neutralizing some of thesulfonic acid groups of the monomer (A2) based on the properties of thebasic compound (B) serves to increase the hydrophilicity of thecopolymer while at the same time enhancing the blushing suppressioneffect and providing excellent heat resistance by suppressing oxidationdegradation of the coating film caused by sulfonic acid groups underhigh temperature conditions. Additionally, good anti-fog properties areachieved by the surfactant effect of the surfactant (C), which reducesthe surface tension of the moisture adhering to the coating film surfaceso as to form a water film.

Thus, with the anti-fog coating composition blushing is suppressed evenwhen the coating material is applied and dried under high-humidityconditions, and heat-curing can be achieved in a short time and at a lowtemperature to obtain a coating film with tight adhesion to a substrateand excellent heat resistance and anti-fog properties.

(2) Moreover, the monomer (A1) is set at 3 to 20 parts by mass, themonomer (A2) at 3 to 20 parts by mass and the monomer (A3) at 60 to 94parts by mass, while the total of the monomer (A1) and the monomer (A2)is set at 6 to 40 parts by mass per 100 parts by mass as the total ofthe monomer (A1), the monomer (A2) and the monomer (A3). As a result,the curing properties based on the monomer (A1) are enhanced by thecatalytic function based on the monomer (A2), while blushing duringapplication can be suppressed by the hydrophilicity based on monomer the(A2). In addition, good heat resistance and adhesiveness of the coatingfilm can be achieved because the content of the monomer (A3) issufficient.

Moreover, the content of basic compound (B) is set at 50 to 95 mol % ofthe sulfonic acid groups in the monomer (A2). This increases thehydrophilicity of the copolymer to provide an adequate blushingsuppression effect while maintaining the catalytic function of thesulfonic acid groups and improving heat resistance by suppressingoxidation degradation of the coating film caused by sulfonic acid groupsunder high-temperature conditions.

Because the content of the surfactant (C) is set at 0.5 to 30 parts bymass per 100 parts by mass of the copolymer (A), moreover, the surfacetension of the moisture adhering to the surface of the coating film isreduced, and this effect is sufficient to form a water film.

(3) When the monomer mixtures also contains theN,N-dialkyl(meth)acrylamide monomer (A4), and the content of the monomer(A4) is set at 5 to 50 parts by mass per 100 parts by mass as the totalof the monomer (A3) and the monomer (A4), the blushing suppressioneffect can be increased still further, and the heat resistance of thecoating film can also be improved.

(4) Because the base dissociation constant pKb of the basic compound (B)in an aqueous solution at 25° C. is 3 to 14, the sulfonic acid groupsand the basic compound are likely to dissociate during heat-curing ofthe coating film, allowing the sulfonic acid groups to fulfill theirfunction as an acid catalyst.

(5) Because the boiling point of the basic compound (B) is 130 to 1500°C., it has low volatility under high-temperature conditions, making theeffect of suppressing oxidation degradation of the coating film causedby sulfonic acid groups under high-temperature conditions morepersistent, and further increasing heat resistance.

EXAMPLES

The aforementioned embodiment is explained in more detail below usingexamples and comparative examples.

Example 1

The following compounds were loaded into a reaction container equippedwith an agitator, a nitrogen introduction pipe and a cooling pipe, andheated at 65° C. under a supply of nitrogen gas.

-   -   240 g of n-propanol (abbreviated as NPA below) as a        polymerization solvent;    -   10 g of N-methylolacrylamide (abbreviated as N-MAA below) as the        monomer (A1);    -   10 g of 2-acrylamido-2-methylpropanesulfonic acid (abbreviated        as AMPS below) as themonomer (A2);    -   60 g of methyl methacrylate (abbreviated as MMA below) and 20 g        of n-butyl acrylate (abbreviated as BA below) as the monomer        (A3);    -   20 g of N,N-dimethylacrylamide (abbreviated as DMAA below) as        the monomer (A4);    -   5.04 g of triethanolamine (see Table 1; boiling point 335° C.,        base dissociation constant pKb=6.2 in an aqueous solution at 25°        C.) as the basic compound (B).

The amount of the basic compound (B) corresponds to 70 mol % of thesulfonic acid groups in the AMPS used as the monomer (A2). See formula:{AMPS loaded}/molar mass of AMPS×70%/100×{molar mass oftriethanolamine}=10/207.4×70/100×149.2=5.04.

Next, a solution of 1 g of a hydrocarbon dilution of t-hexyl peroxidepivalate (Perhexyl PV™, manufactured by NOF Corp.) dissolved in 40 g ofNPA was dripped into the reaction container over the course of 3 hoursas the radical polymerization initiator. After 5 hours ofpolymerization, the temperature of the reaction solution was raised to80° C., and polymerization was performed at that temperature for 1 hourto obtain a solution with a copolymer concentration of 30 mass %.

266.7 g of NPA and 400 g of propylene glycol monomethyl ether(abbreviated below as PGM) were added to 333.3 g of this copolymersolution (100 g as copolymer) to adjust the copolymer concentration to10 mass %, and 10 g (8 g as pure product) of sodium di-2-ethylhexylsulfosuccinate (Rapisol A-80™, NOF Corp., 80 mass % active ingredient)as the surfactant (C) and 0.1 g of polyether denatured polydimethylsiloxane as a leveling agent (BYK Chemical BYK333™) were mixed in toobtain an anti-fog coating composition.

This anti-fog coating composition was evaluated by the methods explainedbelow for evaluating anti-fog coating compositions, with the resultsshown in Table 2.

TABLE 1 Base dissociation constant (pKb) Boiling Molar in an aqueouspoint mass solution at 25° C. (° C.) (g/mol) Basic Triethanolamine 6.2335 149.2 compound Imidazole 7.1 256 68.1 (B) Dimethylamino 4.1 144 89.1ethanol Pyridine 8.8 115 79.1 Triethylamine 3.2 90 101.2 Sodium 0.2 139040.0 hydroxide

TABLE 2 Examples Units 1 2 3 4 5 6 7 8 Monomers A1 N-MAA Mass parts(total of 10 10 10 10 10 10 10 10 forming A2 AMPS monomers (A1) + (A2) +10 10 10 10 10 10 10 10 copolymer A3 MMA (A3) = 100) 60 60 60 60 60 6060 60 BA 20 20 20 20 20 20 20 20 A4 DMAA 20 20 20 20 20 20 20 20 Basic BTriethanolamine Mol % (of sulfonic acid 70 — — — — — 50 95 compoundImidazole groups in monomer (A2)) — 70 — — — — — — Dimethylaminoethanol— — 70 — — — — — Pyridine — — — 70 — — — — Triethylamine — — — — 70 — —— Sodium hydroxide — — — — — 70 — — Surfactant C Rapisol A80 (as pureMass parts (total of 8 8 8 8 8 8 8 8 product) monomers (A1) + (A2) +Other BYK333 (A3) + (A4) = 100) 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 SolventNPA 500 500 500 500 500 500 500 500 PGM 400 400 400 400 400 400 400 400Evaluation Anti-blushing properties

◯

results Necessary curing time (minutes) 10 10 10 10 20 40 10 40Adhesiveness (PC)

Adhesiveness (PMMA)

Anti-fog properties

Heat resistance

◯ Δ Δ

Δ

(1) Evaluation of anti-blushing properties

In an environment set to 30° C., variable relative setting between RH60% and RH 90%, the anti-fog coating composition was applied by spraycoating to a polycarbonate plate to a thickness of 2 to 3 μm of thecoating film after curing, then left as is in the same environment for30 minutes after application. This was then heat-cured for 10 minutes at80° C. to obtain a coating film test piece. Coating film test pieceswere prepared by the aforementioned methods at various relative humidityRH levels between 60% and 90%. The external appearance of the coatingfilm was observed visually, and the maximum relative humidity at whichno whitening or other abnormalities were observed was determined andevaluated according to the following four-grade scale. A grade of xmeans that there were problems for actual use, Δ means that there wereno problems for actual use, ◯ means more desirable and {circle around(x)} means most desirable.

{circle around (x)}: Colorless transparent coating film obtained inenvironment set to 90% RH

◯: Colorless transparent coating film obtained in environment set to 80%RH

Δ: Colorless transparent coating film obtained in environment set to 70%RH

x: Colorless transparent coating film obtained in environment set to 60%RH

(2) Evaluation of necessary curing time

The anti-fog coating composition was applied by spray coating to apolycarbonate plate to a thickness of 2 to 3 μm of the coating filmafter curing, dried for 1 minute at 30° C., and heat-cured at 80° C. forvarious times between 10 and 90 minutes to obtain coating film testpieces. The curing time was varied within the range of 10 minutes, 20minutes, 40 minutes, 60 minutes and a maximum of 90 minutes, theresulting coating film was immersed for 240 hours in warm water at 40°C. and dried for 1 hour at room temperature, and the external appearanceof the coating film was evaluated visually. The minimum curing time atwhich the external appearance of the coating film after warm waterimmersion was the same as before the test was given as the necessarycuring time. A necessary curing time of 40 minutes or less wasconsidered not a problem for actual use, while 20 minutes or less wasconsidered more desirable and 10 minutes or less was extremelydesirable.

(3) Evaluation of Coating Film Performance

The anti-fog coating composition was applied by spray coating to apolycarbonate resin plate and an acrylic resin plate to a thickness of 2to 3 μm of the coating film after curing, dried for 1 minute at 30° C.,and heat-cured at 80° C. for the necessary curing time to obtain acoating film test piece.

(Adhesiveness (PC))

On the coating film test piece formed on the polycarbonate resin (PC)plate, a region of the coating film 1 cm long by 1 cm wide was cut at 1mm intervals to prepare 100 grid squares. Cellophane tape was affixed tothe surface of the grid squares and rapidly peeled off, and externalappearance was observed visually and evaluated according to thefollowing four-grade scale. A grade of x means that there were problemsfor actual use, Δ means that there were no problems for actual use, ◯means more desirable and {circle around (x)} means most desirable.

{circle around (x)}: No peeling

◯: Slight peeling at the intersections of the cuts

Δ: Partial peeling observed

x: Completely peeled

(Adhesiveness (PMMA))

Adhesiveness was evaluated in the same way as adhesiveness (PC) aboveexcept that the resin plate was replaced with an acrylic resin (PMMA)plate.

(Anti-Fog Properties)

The coating film test piece formed on the polycarbonate resin plate oracrylic resin plate was set 5 cm above the water surface of a warm waterbath maintained at 80° C. with the coating film surface of the testpiece facing down, the coating film was continuously exposed to steamfrom the warm water bath, and 10 seconds after exposure the presence orabsence of fog was evaluated visually according to the followingfive-grade scale. A grade of x or xx means that there were problems foractual use, Δ means that there were no problems for actual use, ◯ meansmore desirable and {circle around (x)} means most desirable.

{circle around (x)}: No fog observed

◯: Slight fog observed for a moment immediately after exposure to steam,but not thereafter

Δ: Slight fog observed, or no fog observed but coating film surfaceappeared damaged rather than smooth

x: Obvious fog observed

xx: Coating film turned white immediately after exposure to steam due toinsufficient curing

(Heat Resistance)

The coating film test piece formed on the polycarbonate resin plate wasleft for 240 hours in a 120° C. atmosphere, and then cooled for 1 hourat room temperature. After cooling the aforementioned anti-fog test wasperformed, and the piece was evaluated as described above.

Examples 2 to 8

Copolymer solutions were prepared as in Example 1 except that the typeof the basic compound (B) and the added amount thereof per the sulfonicacid groups in monomer (A2) were changed as shown in Table 2, anti-fogcoating compositions were manufactured, and each was evaluated with theresults shown in Table 2. The physical properties of the basic compounds(B) used in each example are shown in Table 1.

Examples 9 to 17

Copolymer solutions were prepared as in Example 1 but with thecomponents and compounded proportions shown in Table 3, anti-fog coatingcompositions were manufactured, and each was evaluated with the resultsshown in Table 3.

TABLE 3 Examples Units 9 10 11 12 13 14 15 16 17 Monomers A1 N-MAA Massparts (total of 3 20 12 10 3 20 10 10 10 forming A2 AMPS monomers (A1) +(A2) + 12 10 3 20 3 20 10 10 10 copolymer A3 MMA (A3) = 100) 65 60 65 6070 60 — 60 60 2-EHMA — — — — — — 60 — — BA 20 10 20 10 24 — 20 20 20 A4DMAA 20 10 20 10 20 10 20 20 20 Basic B Triethanolamine Mol % (ofsulfonic acid 70 90 — — 70 90 — 70 70 compound Imidazole groups inmonomer — — 70 90 — — 80 — — (A2)) Surfactant C Rapisol A80 (as Massparts (total of 8 8 8 8 8 8 8 0.5 30 pure product) monomers (A1) +(A2) + Other BYK333 (A3) + (A4) = 100) 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.10.1 Solvent NPA 500 500 500 500 500 500 500 500 500 PGM 400 400 400 400400 400 400 400 400 Evaluation Anti-blushing properties

Δ

Δ

Δ

results Necessary curing time (minutes) 20 10 20 10 40 10 10 10 10Adhesiveness (PC)

◯

Δ

Δ Adhesiveness (PMMA)

Δ

Δ

Δ Anti-fog propertiees

Δ

Δ

Δ

Heat resistance

Δ

Δ

Δ

Δ

The symbols in Tables 2 and 3 have the following meanings. N-MAA:N-methylolacrylamide AMPS: 2-acrylamido-2-methylpropanesulfonic acidMMA: Methyl methacrylate 2-EHMA: 2-ethylhexyl methacrylate BA: n-butylacrylate DMAA: N,N-dimethylacrylamide NPA: n-propanol PGM: Propyleneglycol monomethyl ether

As shown in Table 2, in the anti-fog coating compositions of Examples 1and 2 the basic compounds (B) were triethanolamine and imidazole havingpKbs of 6.2 and 7.1 and boiling points of 335° C. and 256° C.,respectively, and the composition of the copolymer and the contents ofthe components were within the more preferred range. As a result, theanti-fog coating compositions of Examples 1 and 2 had extremely goodanti-blushing properties, could be heat-cured at a low temperature in ashort amount of time, and had extremely good coating film performance.

In the anti-fog coating composition of Example 3, the pKb of the basiccompound (B) was 4.1 and the boiling point of the dimethyl amino ethanolwas 144° C., and because the boiling point of the basic compound (B) waslower than in Example 1, the anti-fog coating composition of Example 3had slightly less heat resistance in comparison with Example 1.

In Example 4, the basic compound (B) was pyridine with a pKb of 8.8 anda boiling point of 115° C., and because the boiling point of the basiccompound (B) was lower than in Example 1 the heat resistance was lowerin Example 4 than in Example 1, but this was not a problem for actualuse.

In Example 5, the basic compound (B) was triethylamine with a pKb of 3.2and a boiling point of 90° C., and because the pKb of the basic compound(B) was lower than in Example 1, the necessary curing time was longer inExample 5 than in Example 1. Moreover, because the boiling point of thebasic compound (B) was lower in Example 5 than in Example 1 the heatresistance was lower in Example 5 than in Example 1, but this was not aproblem for actual use.

In Example 6, the basic compound (B) was sodium hydroxide with a pKb of0.2 and a boiling point of 1390° C., and because the pKb of the basiccompound (B) was lower than in Example 1, the necessary curing time waslonger in Example 6 than in Example 1, but this was not a problem foractual use.

Because the amount of the triethanolamine used as the basic compound (B)was at the lower limit of the preferred range in Example 7, theanti-blushing properties of Example 7 were slightly inferior to those ofExample 1 and heat resistance was less, but this was not a problem foractual use.

Because the amount of the triethanolamine used as the basic compound (B)was at the upper limit of the preferred range in Example 8, thenecessary curing time was longer in Example 8 than in Example 1, butthis was not a problem for actual use.

As shown in Table 3, because the content the of monomer (A1) was at thelower limit of the preferred range in Example 9, the curing propertiesof the copolymer were reduced and the necessary curing time was slightlylonger.

In Example 10, because the content of the monomer (A1) was at the upperlimit of the preferred range, the crosslinking density of the copolymerwas higher, detracting from the anti-fog properties of the coating filmand reducing heat resistance, but this was not a problem for actual use.

In Example 11, because the content of the monomer (A2) was at the lowerlimit of the preferred range, the hydrophilicity and curing propertiesof the copolymer were reduced, the anti-blushing effect was less, andthe necessary curing time was slightly longer, but this was not aproblem for actual use.

In Example 12, because the content of monomer (A2) was at the upperlimit of the preferred range, the polarity of the copolymer wasincreased and affinity between the coating film and the substrate wasreduced, resulting in a loss of adhesiveness and reduced heatresistance, but this was not a problem for actual use.

In Example 13, because the total of the monomer (A1) and the monomer(A2) was at the lower limit of the preferred range, while the content ofthe monomer (A3) was at the upper limit of the preferred range, thehydrophilicity and curing properties of the copolymer were reduced, theanti-blushing effect was less and the necessary curing time was longer,but this was not a problem for actual use.

In Example 14, the total of the monomer (A1) and the monomer (A2) was atthe upper limit of the preferred range while the content of the monomer(A3) was at the lower limit of the preferred range. Thus, the polarityof the copolymer was increased and affinity between the coating film andthe substrate was reduced, resulting in a loss of adhesiveness and areduced anti-fog effect, and the crosslinking density of the copolymerwas also higher, detracting from the anti-fog properties of the coatingfilm and reducing heat resistance, but this was not a problem for actualuse.

In Example 15, the hydrophilicity of the copolymer and the anti-blushingproperties were reduced because the MMA (with 1 carbon atom in the alkylgroup of the alkyl ester) of Example 1 was replaced with 2-EHMA (with 8carbon atoms in the alkyl group of the alkyl ester) as the monomer (A3),but this was not a problem for actual use.

In Example 16, because the content of surfactant (C) was at the lowerlimit of the preferred range, the ability to form a water film was lessthan in Example 1 and the anti-fog properties were reduced, but this wasnot a problem for actual use.

In Example 17, adhesiveness was less than in Example 1 because thecontent of the surfactant (C) was at the upper limit of the preferredrange, but this was not a problem for actual use.

The invention claimed is:
 1. An anti-fog coating composition comprising:a copolymer (A) formed from a monomer mixture containing a monomer (A1),a monomer (A2) and a monomer (A3) shown below; a basic compound (B); anda surfactant (C), wherein: the monomer (A1) is a vinyl monomer havingN-methylol group, the monomer (A2) is a vinyl monomer having sulfonicacid group selected from the group consisting of3-sulfopropyl(meth)acrylate, 2-sulfoethyl(meth)acrylate,2-acrylamido-2-methylpropanesulfonic acid, and a combination thereof,the monomer (A3) is an alkyl(meth)acrylate monomer in which the numberof carbon atoms in the alkyl group is 1 to 4, the content of the monomer(A1) is 3 to 20 parts by mass, the content of the monomer (A2) is 3 to20 parts by mass, the content of the monomer (A3) is 60 to 94 parts bymass, and the total of the monomer (A1) and the monomer (A2) is 6 to 40parts by mass per 100 parts by mass as the total of the monomer (A1),the monomer (A2) and the monomer (A3), the content of the basic compound(B) is 50 to 95 mol % relative to 100 mol % of the sulfonic acid groupin the monomer (A2), and the content of the surfactant (C) is 0.5 to 30parts by mass per 100 parts by mass of the copolymer (A), a basedissociation constant of the basic compound (B) in an aqueous solutionat 25° C. is 3 to 14, and a boiling point of the basic compound (B) is130° C. to 1500° C.
 2. The anti-fog coating composition according toclaim 1, wherein the monomer mixture further contains aN,N-dialkyl(meth)acrylamide monomer (A4), the content of the monomer(A4) being 5 to 50 parts by mass per 100 parts by mass as the total ofthe monomer (A3) and the monomer (A4).
 3. The anti-fog coatingcomposition according to claim 1, wherein the copolymer (A) hascrosslinked structures formed by a condensation reaction of N-methylolgroup of the monomer (A1), and the content of the basic compound (B) ispredetermined so that the monomer (A2), after neutralized by the basiccompound (B), has neutralized sulfonic acid group that improves thehydrophilicity of the copolymer (A) and non-neutralized sulfonic acidgroup that promotes the condensation reaction of the monomer (A1).